1. Climate Change: The Ocean’s Response
Richard J. Cowlishaw, Ph.D
Southwestern College
Winfield, KS

2. Key Threats to Ocean Ecosystems
International Programme on the State of the Ocean (IPSO) report highlights key threats to ocean ecosystems
Pollution
Bycatch
Overfishing
Eutrophication
Aquaculture
Habitat Alteration
Invasive Species
Coastal Development
Climate Change

3. The Big Heat Sponge
Oceans have absorbed 90% of the heat generated by humans
Heat capacity of the ocean has limits
Atmospheric warming will accelerate when limit is reached
Nuccitelli et al. 2012

4. Deep Ocean Heating Heat penetrates to ocean depths over time
Glecker et al., 2016
Nature Climate Change
Large volcanic eruptions in the past (black triangles) have a cooling effect on the atmospheric and ocean temperature.
Small simulated eruptions have little effect.
Half of the forced heating of the ocean has occurred since 1997, reflecting the recent acceleration of the planet’s warming.
Heat penetrates to ocean depths over time

5. Warming Impacts on the Ocean
Alteration of surface currents
Weakening of thermohaline currents
Strengthening of permanent thermocline
Sea-level rise

6. Ocean Circulation Surface winds drive movement of water
Surface currents distribute heat between equator and poles
Spherical shape of planet and its rotation causes currents to deflect along their path
Right deflection in Northern Hemisphere
Left deflection in Southern Hemisphere
Establishes ocean gyres

7. Ocean Surface Circulation
Warm air/water to north, cold air/water to south

8. Europe: So North Yet So Temperate
Gulf Stream – conveyor of heat to high latitudes

9. Deep Ocean Currents Super-cooling at the poles
Cooling and ice formation  increased density
Cold, oxygen-rich water sinks to depth
Forms deep bottom water currents
Thermohaline currents

10. Overturning of the ocean volume on a 1000-year scale

11. Reducing Ocean Circulation
Decreasing temperature differences between poles and equator – weakens or alters surface currents
Potential cool down Europe – weakening of Gulf Stream
Freshwater from melting ice reduces seawater density  reduces bottom water formation
Reduce the amount of oxygenated water at depth – threat of hypoxia in deep ocean

12. Strengthening Thermocline
Thermocline – depth interval of rapid temperature change
Density gradient
Separates surface waters from the deeper ocean
Warming air temperatures will likely strengthen it
Reduce primary production and CO2 uptake by ocean
(Cold)
Dissolved Nutrients
(Warm)
Light

13. Sea-Level Rise Average sea level rising 1.5-2.0 mm annually
21st century projections: mm ( inches)
Ways sea-level can rise with global warming
Melting of land ice sheets and glaciers
Thermal expansion – warm water occupies greater volume than cold water
Uncertainties on how much and when
>600 million people at risk by rising seas

14. IPCC 2014 Sea Level Rise Projections
Past and future sea-level rise. For the past, proxy data are shown in light purple and tide gauge data in blue. For the future, the IPCC projections for very high emissions (red) and very low emissions (blue,) are shown. Source: IPCC AR5 Fig

15. Correlation of CO2 and Sea-level
Figure is somewhat dated. CO2 concentrations have recently crossed the 400 ppm mark, ahead of the 2020 projection.
We can infer that temperature levels rose and fell with CO2 levels across this time line. Rise and fall of CO2 reflect the sequence of interglacial and glacial periods respectively

16. Ocean Acidification CO2 uptake by oceans has two consequences:
Offset human-produced CO2 emissions
Increase the acidity of the oceans
Ocean pH has decreased by 0.1 pH units since 1860  30% increase in acidity

17. Predicted Impacts on Marine Life
Increasing water temperatures
Changes in timing and location of primary production – decrease in food predictability
Change in ranges and migration patterns
Mobile species - Relocation to cooler waters
Sessile species – tolerate, evolve or die
Coral bleaching and die-back
Increased threat of water-borne diseases
Increasing hypoxia in deeper waters

18. Predicted Impacts on Marine Life
Increasing acidity
Reductions in calcifying organisms, those with calcium carbonate structures (i.e. shells)
Span the food chain: algae, protozoa, zooplankton, corals, echinoderms, crustaceans, molluscs
Blood acidosis; reduced metabolic rates
Suppressed immune systems
Impaired olfaction and feeding behavior
Noisier ocean – problems of sound-dependent species

19. The Sixth Great Extinction Event
Permian Extinction (The Great Dying)
252 million years ago
96% of all marine species and 70% of all terrestrial species went extinct
Causes? Not clear, but climate change and change in ocean circulation was certainly in the mix
Evidence that the next great extinction event is underway
Major difference: Brought upon by another species (humans)

20. An Ocean in Crisis We’ve arrived at the tipping point for the oceans
Oceans are big but have limits – we are realizing those limits
One billion people unsustainably rely on the oceans for their protein – what will 2050 look like?
Without action on climate change we will push the Sixth Mass Extinction forward